What new set of rules does Willimena live by in this adventure? Well, summer's over, and Willie is finally about to enter the third grade. Things are looking pretty rosy until she learns that Mrs. Sweetly-who's anything but sweet-is going to be her teacher for the whole year. Not to be daunted, Willie wonders how she can make a good impression on the "sinister" Mrs. Sweetly. And, as Willie soon finds out, the first rule to losing your class pet (and impressing your teacher) is to "volunteer to bring your class pet home." Rule #2? "Make sure you look away while cleaning his cage in your backyard". And so, when Lester, the third grade's beloved floppy-eared guinea pig makes a break for it, Willimena's rules are about to change.